This invention relates to an all solid state fuel cell structure and more particularly to a fuel cell made from a series of porous and partially porous semiconductor structures employing silicon and/or silicon carbide.
Like the conventional dry cell and lead acid batteries, fuel cells work by virtue of electrochemical reactions in which the molecular energy of the fuel and an oxidant are transformed into direct current electrical energy. Fuel cells do not consume chemicals that form part of their structure or as stored within a structure. They react with fuels supplied from outside the cell. Since the fuel cell itself does not undergo an irreversible chemical change, it can continue to operate as long as its fuel and oxidant are supplied and byproducts removed, or at least until electrodes cease to operate because of mechanical or chemical deterioration.
A fuel cell basically consists of a container of an electrolyte. For example, the electrolyte can be a water solution of an acid, such as phosphoric acid, or a similar acid. In this solution are immersed two porous electrodes and through these the reactants, as hydrogen and oxygen, are brought into contact with the electrolyte. The hydrogen and oxygen react to release ions and electrons, and water is produced. The electrons are made to do useful work in an external circuit, whereas the ions flow from one electrode to the other to complete the internal circuit in the cell. The operation of fuel cells is very well understood. See, for example, a publication by NASA entitled, xe2x80x9cFuel Cellsxe2x80x94A Surveyxe2x80x9d, NASA SP-5115 published in 1973. Every fuel cell uses an input fuel which is catalytically reacted (electrons removed from the fuel elements) in the fuel cell to create an electric current. Every fuel cell consists of an electrolyte material which is sandwiched between two porous electrodes as the anode and cathode. The input fuel passes through the anode (oxygen through the cathode) where it is split into ions and electrons. The electrons go through an external circuit while the ions move through the electrolyte to the oppositely charged cathode. At the cathode, the ions combine with oxygen to form H2O and depending on the fuel, carbon dioxide (CO2).
Thus, at the anode H2xe2x86x922H++2exe2x88x92
and at the cathode                     1        2            ⁢              O        2              +          2      ⁢              H        +              +          2      ⁢              e        -              ->            H      2        ⁢    O  
In most fuel cells platinum, which coats both the anode and cathode, the side adjacent to the electrolyte serves as a catalyst for the oxidation and reduction processes. Fuel and oxidant gases are supplied to the back of the anode and the cathode respectively, and both the anode and cathode are electrically conductive. Fuel is supplied to the backside of the anode and oxygen is supplied to the backside of the cathode. In addition, both on the anode and on the cathode side there is an exit hole to permit the egress of either fuel or extra oxygen and on the cathode side (the reaction byproducts), as water (as steam) and/or carbon dioxide CO2. Thus, fuel cells are very well known and operation is continued to be improved. See, for example, an article in Popular Science, March 2002, Volume 260, No. 3, page 61 entitled, xe2x80x9cDreams of the New Powerxe2x80x94A Fuel Cell in Every Homexe2x80x9d. That article describes the problems with fuel cells, as well as the operation of fuel cells and the attempt to reduce the costs of fuel cells.
It is therefore an object of the present invention to provide an improved fuel cell which is all solid state and which fuel cells exhibit improved high temperature operation.
A solid state fuel cell is fabricated from three substructures. There is a porous anode made from n+ silicon which is surrounded by a non-porous ring. The pore size of the anode material is sufficiently large to allow hydrogen gas to flow through and is of a sufficiently high conductivity to easily permit current flow of electrons. One side of the anode has enlarged pores and a layer of titanium and platinum is sputtered or otherwise deposited on the surface with the enlarged pores to produce a coated surface. A cathode is made in a similar manner and is fabricated as the anode. There is a center electrolytic section made from a low conductivity silicon or silicon carbide. The center electrolytic section has the coated side of the anode secured to one side and has the coated side of the cathode secured to the other side. The other or un-coated face of both the anode and the cathode has an electrical contact secured thereto to permit electrons to leave the anode and to reenter the cathode. The electrolytic center structure is filled with an ionic conductor. In this manner, hydrogen is broken into ions and electrons. The electrons cause a current flow, while the ions react with oxygen and produce water which is discharged from the fuel cell as steam or vapor.